1. Field of the Invention
The present invention relates to an optical element having the functions of diffraction, branching, filtering, and the like and used mainly in optical communications, and a method of fabrication thereof.
2. Related Art of the Invention
In recent public telecommunication and computer networks, optical communications having broadband capability is widely used in order to improve the speed and performance. Further, widely spreading are optical communications systems using wavelength division multiplexing and interactive (two-way) transmission.
In the optical communications industry, various optical integrated circuits having diverse functions are now under development for the application of sophisticated optical signal processing. An essential element in the optical integrated circuits is an optical waveguide. The optical waveguide is a device in which a core region having a higher refractive index is surrounded by a clad layer having a lower refractive index, whereby light is constrained within the core region and propagates therethrough. In the optical waveguide, various functions of diffraction, branching, filtering, and the like are implemented by arrangement of a core pattern. In particular, quartz optical waveguides have various advantages of low power loss, physical and chemical stability, and good matching with optical fibers, and are used as typical passive optical waveguides.
In a typical method of fabrication of optical waveguides, a flame sedimentation technique is used for core/clad film formation, while a reactive ion etching technique is used for core pattern formation. For the core/clad film formation, proposed techniques other than the flame sedimentation technique are a CVD technique, a vacuum deposition technique, a sputtering technique, and the like.
Nevertheless, in such optical modules, there have been the following problems in cost and productivity.
Although many methods are proposed, at present, there is no method of fabrication of optical waveguides satisfying sufficient performance, mass-productivity, and low cost condition. This is because each method of film formation has advantages and disadvantages. For example, in the flame sedimentation technique and the CVD technique, high quality core is obtained. Nevertheless, the flame sedimentation technique requires a plural times of high temperature annealing at 1,000xc2x0 C. or higher during about ten hours. On the other hand, the CVD technique has disadvantages such as a smaller film formation area in mass-productivity. Further, the electron beam (vacuum) deposition technique and the sputtering technique realize the formation of low power-loss film. Nevertheless, the slow film formation rate of these techniques causes a problem in cost, because the film thickness of 10 xcexcm to a few tens xcexcm is generally necessary in the fabrication process of optical waveguides.
FIG. 11 is a diagram showing an example of a prior art method of fabrication of an optical element.
First, quartz material 114 to serve as a core is sedimented onto a substrate 111 by flame sedimentation technique (FIG. 11(a)). The quartz material 114 has a refractive index higher than that of the substrate 111, whereby the material works as an optical waveguide. Next, photoresist 118 is applied onto the quartz material 114 (FIG. 11(b)), and then undergoes baking process, exposure process under a photomask having a desired pattern, and development process. Then, the photoresist 118 is patterned (FIG. 11(c)).
Then, the quartz material 114 together with the substrate 111 undergoes etching process, thereby being patterned. At that time, the photoresist 118 serves as a mask, thereby causing the quartz material 114 to have a desired pattern (FIG. 11(d)). After that, the photoresist 118 of mask is removed (FIG. 11(e)) Similarly, photoresist is applied onto the patterned portion, and then undergoes exposure process under a photomask having a periodical pattern, development process, and etching process. Then, periodical grooves are formed in the patterned portion, and hence a desired optical element is obtained (FIG. 11(f))
Taking the above-mentioned problems in the conventional method of fabrication of optical elements onto consideration, an object of the present invention is to provide an optical element satisfying sufficient performance, mass-production capability with low cost condition, and a method of fabrication thereof.
One aspect of the present invention is an optical element comprising: a substrate having or not having a channel for optical waveguide; and a material which has a refractive index higher than that of said substrate and is filled in said channel for optical waveguide or is disposed on said substrate; wherein
the refractive index in a part of said material varies substantially periodically or is substantially continuously monotone increasing or decreasing in the direction of light propagation.
Another aspect of the present invention is an optical element the refractive index in a part of said material varies substantially periodically or is substantially continuously monotone increasing or decreasing in the direction substantially perpendicular to said direction of light propagation.
Still another aspect of the present invention is an optical element comprising: a substrate having or not having a channel for optical waveguide; and a material which has a refractive index higher than that of said substrate and is filled in said channel for optical waveguide or is disposd on said substrate; wherein
the refractive index in a part of said material varies substantially periodically or is substantially continuously monotone increasing or decreasing in a direction substantially perpendicular to the direction of light propagation.
Yet still another aspect of the present invention is an optical element comprising: a substrate having or not having a channel for optical waveguide; and a resin which has a refractive index higher than that of said substrate and is filled in said channel for optical waveguide or is disposed on said substrate; wherein
the refractive index in a part of said resin varies in the direction of light propagation and/or in a direction substantially perpendicular to said direction of light propagation.
Still yet another aspect of the present invention is an optical element according to 4th invention, said part of resin the refractive index of which varies is formed using the photo-hardening or thermo-hardening property of said resin.
A further aspect of the present invention is an optical element comprising: a substrate having or not having a channel for optical waveguide; and a material which has a refractive index higher than that of said substrate and is filled in said channel for optical waveguide or is disposed on said substrate; wherein
said optical element further comprises temperature controlling elements disposed on said material and for partially changing the temperature of said material in the direction of light propagation and/or in a direction substantially perpendicular to said direction of light propagation.
A still further aspect of the present invention is an optical element comprising: a substrate having or not having a channel for optical waveguide; and a material which has a refractive index higher than that of said substrate and is filled in said channel for optical waveguide or is disposed on said substrate; wherein
said optical element further comprises electrodes disposed on said material and for partially changing the electric field in said material in the direction of light propagation and/or in a direction substantially perpendicular to said direction of light propagation.
A yet further aspect of the present invention is an optical element comprising: a substrate having or not having a channel for optical waveguide; and a material which has a refractive index higher than that of said substrate and is filled in said channel for optical waveguide or is disposed on said substrate; wherein
said optical element further comprises a part where said material protrudes to the direction of said substrate and/or a part where said substrate protrudes to the direction of said material, in the direction of light propagation and/or in a direction substantially perpendicular to said direction of light propagation.
A still yet further aspect of the present invention is an optical element, wherein said protruding parts are provided substantially periodically.
An additional aspect of the present invention is an optical element, wherein said material is composed of glass material or resin.
A still additional aspect of the present invention is in a method of fabrication of optical element, wherein photo-hardening resin is formed in a substrate, and wherein light is irradiated onto said photo-hardening resin, thereby hardening said photo-hardening resin, a method of fabrication of optical element wherein the amount of said light irradiated onto the surface of said photo-hardening resin is varied.
A yet additional aspect of the present invention is a method of fabrication of optical element, wherein the amount of said light irradiation is varied substantially periodically or is substantially continuously monotone increasing or decreasing, in a predetermined direction on the surface of said photo-hardening resin.
A still yet additional aspect of the present invention is a method of fabrication of optical element, wherein the intensity of said light irradiation onto said photo-hardening resin is varied, whereby the amount of said light irradiation onto the surface of said photo-hardeninkresin is varied.
A supplementary aspect of the present invention is a method of fabrication of optical element, wherein a mask having partially different light transmissivity is used, whereby the intensity of said light irradiation onto the surface of said photo-hardening resin is varied.
A still supplementary aspect of the present invention is a method of fabrication of optical element, wherein a light shielding plate is used so as to sequentially change the region irradiated by said light, whereby the amount of said light irradiation onto is varied.
A yet supplementary aspect of the present invention is in a method of fabrication of optical element, wherein photo-hardening resin is formed in a substrate, and wherein light is irradiated onto said photo-hardening resin, thereby hardening said photo-hardening resin, a method of fabrication of optical element, wherein another optical component is connected to said photo-hardening resin, and then said photo-hardening resin is hardened, whereby said optical component is fixed to said photo-hardening resin.
A still yet supplementary aspect of the present invention is a method of fabrication of an optical element, wherein said channel for optical waveguide in said substrate is formed in a integrated manner using a mold having rotrusion and recess in the surface thereof.
Another aspect of the present invention is a method of fabrication of an optical element, wherein the protrusion and recess in said substrate of said optical element is formed in a integrated manner using a mold having protrusion and recess in the surface thereof.